(a) Field of the Invention
The present invention relates to a method for fabricating a member of vehicle and a side member produced by the same, and more particularly to a method for fabricating a member of vehicle and a side member produced by the same so as to stabilize an absorption directivity of collision energy by fabricating a high-rigidity member for vehicle formed of a martensite organization through a hot stamping mold process with a boron steel, and fabricating a metal organization provided a partial low-rigidity and an improved toughness.
(b) Description of the Related Art
Generally, various safety tests are performed in case of developing a new vehicle in a vehicle company in order to verify quality thereof based on whether the performance thereof satisfies a predetermined standard.
Since the safety relates life of a rider, it is very important for the vehicle to be verified, and then various countries applying a strict standard to the safety of the vehicle.
In this safety test, especially, a front side member of vehicle SM for preparing against frontal crash of the vehicles, as shown in FIG. 1, a bumper beam is mounted at a front end thereof through a crash box 1 and stay 3, and a dash panel 7 is welded to a center thereof and a front end of rearward assembled to a center side member 9.
The front side member SM transfers a residual collision energy F to the vehicle body after a primary collision energy F is absorbed by the bumper beam 5.
Meanwhile, a conventional front side member SM includes an inner member 11 and an outer member 13 formed of steel series of metal sheet pressed, and it is limited to satisfy the rigidity and light-weight at the same time.
Therefore, a new mold method and an ultra-light material capable of simultaneously providing high-rigidity and light-weight have been studied.
As a result of the studies for applying to the front side member SM, a roll forming replaced with a press stamping, and which can mold an ultra high-tensile force steel plate, and thereby a weigh thereof is reduced by 15% or more in comparison with a conventional press production.
Further, tailor welded blank which fabricates a customized blank having a different material, thickness, rigidity, and a tailor rolled blank technology, hydroforming technology molding integrally are applied.
Particularly, as shown in FIG. 2, hot stamping technology which is a hot press mold method using a boron steel plate 15 has been studied.
That is, the hot stamping is such a manner which the boron steel plate 15 is heated at a proper temperature (i,e. approximately 900° C.) so as to form the product in a press mold 17 at one time, and thereby the product is fabricated as a high-rigidity product 19 through a quick cooling.
Herein, the boron steel plate 15 is such as a steel plate where a little quantity of boron is added, and nucleation of free ferrite is suppressed in order to improve hardenability thereof by which the boron is segregated at an atomic level in austenite grain boundary under proper temperature, and decreases free energy in the austenite grain boundary.
As to the hot stamping mold, instead of the manner using a conventional high-rigidity steel, after the boron steel plate of ferrite organization having a tensile strength of 500 MPa to 800 MPa approximately before forming is formed at a temperature more than 900° C. through an austenitation, a martensite organization M having a high-tensile strength of 1300 MPa to 1600 MPa through a quick cooling is obtained.
Herein, the product formed by the hot stamping forming has an advantage of a light-weight and a high-rigidity through which a rigidity of the product may be 4 to 5 times more than that of normal steel plate, and also a weight thereof can be reduced by 40% comparably.
However, if the product formed by the hot stamping forming is applied to a bumper beam 5 which should absorb a collision energy effectively through improved rigidity in comparison with the conventional steel plate, or the front side member SM and like that, the absorption performance of collision energy is incomplete despite of a high-rigidity and a light-weight.
In case of the front side member SM, it is important for an absorption directivity of collision energy to evenly distributing the collision energy to the vehicle body.
Herein, in case of applying the front side member SM to high-rigidity through the hot stamping mold, safety of the vehicle is deteriorated due to partial buckling rather than sequential absorption.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.